Annealing furnace



1960 H. J. KURTZ ETAL 2,948,797

ANNEALING FURNACE Filed Jan. 30, 1959 2 4 a 8 r /0 /2 /4 /e /&

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3 HE/VPV J AUPTZ BY ALFRED M/LES' 5 Tragp/E v- United States Patent ANNEALING FURNACE Henry J. Kurtz, Terrace Park, and Alfred Miles, Cin- Filed Jan. 30, 1959, Ser. No. 790,190

2 Claims. (Cl. 219--10.79)

This invention relates to annealing furnaces and more particularly to annealing furnaces which provide uniform heat treatment for hollow members or tubes.

Prior annealing furnaces which were employed to heat treat a single hollow member produced initial heating on the outer surface of the member. While the object of such heat treatment was to render the member less brittle, a temperature gradient existed from the outer surface to the inner surface of the member which produced undesir-able thermal stresses in the material. It was. a further problem to provide uniform heat treatment for a plurality of concentric hollow members since the temperature of the various members varied in accordance with position of the member in relation to the heating coils. Thus, thermal stresses might be created in the outermost hollow members while the inner members were subjected to a desired heat treatment.

The present invention provides an improved annealing furnace which heat treats hollow members internally and uniformly without creating undesirable thermal stresses in the members.

It is an object of our invention to provide an improved annealing furnace which produces uniform internal heat treatment of a hollow member.

It is another object of the invention to provide an improved annealing furnace which heat treats uniformly a plurality of concentric hollow members.

It is a further object of the invention to provide an improved annealing furnace in which magnetic cores of different cross sectional area are employed to produce uniform heat treatment at different power levels.

In carrying out our invention in one form, "an annealing furnace is provided which comprises an outer insulated tube, a plurality of induction heating coils surrounding the outer tube, an inner insulated tube positioned concentrically within the outer tube and spaced therefrom, a magnetic core positioned within the inner tube, a coolant passage located between the inner surface of the inner tube and the outer surface of the core, and the inner tube adapted to support a hollow member therearound.

These and other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a sectional view of an annealing furnace embodying our invention;

Fig. 2 is a sectional view taken on line 2--2 of Fig. 1; and

Fig. 3 is a graph plotting total power in kilowatts versus relative ring power density.

In Fig. 1 of the drawing, an annealing furnace shown generally at 10, comprises an outer insulating tube 11 surrounded by a plurality of hollow copper induction heating coils 12 which are water cooled and provided with power from a generator (not shown). Tube 1 1 is .made of a suitable insulation material such as Refrax,

which is manufactured by the Carborundum Company .and described generally as premium grade, dense, bonded silicon carbide refractories. An inner insulating tube 13, which is made of material similar to tube 11, is positioned concentrically within tube 11 and supported by any suitable means (not shown). Within tube 13 is a magnetic core 14 which is spaced at least partially from the inner surface of inner tube 13 to provide a coolant passage therebetween. Magnetic core 14, which is composed. of a metallic conductor such as, laminated iron, a laminated structure or a plurality of individual core elements. v

A single member or a plurality of hollow members is supported on the outer surface of tube 13 to be heat treated within annealing furnace 10. In Figs. 11 and 2 a plurality of concentric hollow members 15, 16, 17, and 18 are shown within furnace 10. A generator which supplies power to induction heating coils 12. is of a suitable power rating to provide the necessary total power. It. is further desirable to have induction heating coils 12 located as close as possible to the hollow members.

We discovered that if core 14 of high magnetic permeability was positioned within insulated tube 13 and kept cooled below the Curie point, the ordinary induction air core transformer circuit produced without tube 13 or core 14 would be converted into a short-circuited, multiple turn secondary, magnetic transformer. We discovered further that the magnetic flux field distribution would be concentrated within centermost member '15 providing the saturation point of the magnetic core was not exceeded. Thus, the power density generated in each member varied inversely as a function of their diameters. We found also that the cross sectional area or material of magnetic core 14 could be varied to affect the magnetic flux distribution linking members 15, 16, 17, and 18 to provide a uniform distribution of power generation or heat treatment in each of these members. Uniform power distribution is more readily obtained when core 14 extends beyond the ends of members 15-18 by a distance equal approximately to the radius defined by the distance from the outer surface of inner tube 13 to the outer surface of member 18.

As is best shown in Fig. 3, the total power provided to coils 12 from a generator (not shown) measured in kilowatts is plotted against relative member power density. Members '15, I16, 17, and 18 identified on this graph are shown in Figs. 1 and 2. A magnetic laminated iron core 14 having an area of 0.066 inch 2 is employed in Figs. 1-3. At a total power of 6 kilowatts to coils 12, an almost uniform power density or heat treatment is afforded to members 15, 16, 17, and 18. Furthermore, we discovered that if the core area of this same material was increased to 0.132 inch such nearly uniform power generation in members 15-18 would be obtained at approximately '19 kilowatts of total power generation.

In the operation of annealing furnace '10, a plurality of concentric hollow member 15-18 are supported around the outer surface of inner insulated tube 13 to receive uniform internal heat treatment. Tube 13 was positioned within outer insulated tube 10 and surrounded by a plurality of induction heating coils 12. A magnetic laminated iron core 14 was positioned within inner tube 13 and provided with a coolant passage between its outer surface and the inner surface of tube 13. Core 14, which had a cross sectional area of 0.066 inch extended beyond the ends of members 15-18 by a distance equal approximately to the radius defined by the distance from the outer surface of tube 13 to the outer surface of member 18. Air was employed as the coolant, which was forced by suitable means (not shown) through the passage between core 14 and tube 13 to retain core 14 below its Curie point. It will be appreciated that other coolants are suitable in the practice of the present invention. 8 kilowatts of total power was supplied by a 50- Patented Aug. 9, 1960 3 kilowatt generator to coils 12 of furnace 10. Each of the members 15-18 received nearly uniform power distribution or heat treatment of 2 kilowatts.

While other modifications of the invention and variation of apparatus which may be employed within the scope of the invention have not been described, the invention is intended to include all such as may be embraced within the following claims.

"What we claim as new and desired to secure by Letters Patent of the United States is:

1'. An annealing furnace comprising an outer insulated tube, induction heating means surrounding said outer tube, an inner insulated tube positioned concentrically within the outer tube and spaced therefrom, a magnetic core positioned within the inner tube, said inner tube provided with a coolant passage, said inner tube adapted to support a hollow member therearound, and said core extending Ibeyond the ends of said member by a distance equal approximately to the radius defined by the distance from the outer surface of said inner tube to the outer surface of said member.

2. An annealing furnace comprising an outer insulated 4 tube, a plurality of induction heating coils surrounding said outer tube, an inner insulated tube positioned concentrically within the outer tube and spaced therefrom, a magnetic laminated iron core positioned within the inner tube, said inner tube provided with a coolant passage located between the outer surface of said core and the inner surface of said inner tube, said inner tube adapted to support a hollow member therearound, and said core 2 extending beyond the end of said member by a distance equal approximately to the radius defined by the distance from the outer surface of said inner tube to the outer surface of said member.

Beck Feb. 11, 

